A lawn cart is probably fine. Look for something w/ larger wheels and a strong rigid frame that you can fasten stuff to. Also I'd go w/ a two wheeled cart rather than a wagon - easier to work with.

I already have a cart, but if I were looking for an inexpensive do-it-yourself option, I'd take a look at a Magna Cart. These are collapsing hand trucks with a wide platform. They're light and inexpensive, and they're seem to be well made.